This proposal attempts to localize antigens from dental plaque microorganisms and antibody to the antigens in gingiva from human subjects with periodontitis. The presence of immune complexes will also be sought. The major technique in the search is immunofluorescence. Additionally, ultrastructural studies will be conducted for antigens localized at the light microscopic level. The overall objective is to contribute to an improved understanding of the etiology of periodontitis, as immune factors related to plaque antigens have been suggested as important to the disease process.